Hydrogen appears to be a very promising fuel for the energy needs of mankind. Use of hydrogen fuels would require only minor modifications to existing engine and power plant designs. In alternative propulsion technologies, such as electric vehicles, hydrogen can be used in fuel cells.
One problem with hydrogen, however, is the safe handling of it. The use of hydrogen as a fuel for widespread distribution in either gaseous or liquid form poses numerous safety, technical, and economic problems that make its use as a fuel prohibitively difficult. In the absence of a hydrogen pipeline network, small-scale users purchase commercial hydrogen as compressed gas in steel cylinders, or as liquid hydrogen in cryogenic containers. One approach to resolve the drawbacks of hydrogen as a fuel includes considering less expensive, simpler, and cheaper materials that can act as a hydrogen carrier and generate hydrogen on demand.
Several on-site methods of producing hydrogen are known, including, reforming of natural gas or hydrocarbons; using permeators to selectively separate hydrogen from ammonia synthesis processes (U.S. Pat. Nos. 4,180,552 and 4,180,553), water electrolysis, and ammonia dissociation or cracking. Reformers have existed to thermally decompose ammonia to produce hydrogen (U.S. Pat. No. 4,704,267). However, the reformers must create heat in closed spaces, which leads to substantial amounts of heat losses. Additionally, heat reformers have inherent limitations as to where they can be used.
Ammonia has been identified as a suitable hydrogen carrier. Ammonia is essentially non-flammable and is readily obtained and handled without need for expensive and complicated technology. In addition, ammonia contains 1.7 times as much hydrogen as liquid hydrogen for a given volume. Compared to liquid hydrogen, ammonia therefore offers significant advantages in cost and convenience as a fuel due to its higher density and its easier storage and distribution. Ammonia is produced and distributed worldwide in millions of tons per year. Procedures for safe handling have been developed in every country. Facilities for storage and transport by barges, trucks and pipelines from producer to ultimate consumer are available throughout the world. Further advantages of ammonia for fuel cells are given in an easy cracking device. Ammonia can be cracked into hydrogen and nitrogen in a suitable separation unit according to the reaction: 2 NH3→3 H2+N2.
Alternatively, natural gas, primarily CH4 or methane which, though difficult to store, is widely available through pipelines and can be cracked similarly. The cracking reaction is: CH4→C+2H2, with carbon being removed as soot.